1. Field Of The Invention
This invention relates generally to developing apparatus, and more particularly is directed to an apparatus for developing an image or picture on a sheet of developing paper from an exposed sheet of photo-sensitive material by pressing together the sheets.
2. Description of the Prior Art
It is known, for example, as disclosed in Japanese laid-open Patent Gazette No. 59-30537, to print or develop a color picture on a sheet of developing paper from a sheet of photo-sensitive material having a coating of photo-sensitive microcapsules which have been irradiated with a light image of the picture. This known printing method employs, as the photo-sensitive sheet, a base made of a suitable resin on which there is a coating of uniformly distributed yellow, magenta and cyan microcapsules. Each of the yellow, magenta and cyan microcapsules has an outer shell of a relatively soft material in which there is sealed an optically-hardening composition containing a respective pigment or a precursor thereof. When the photo-sensitive microcapsules are irradiated with respective wave lengths of light, the optically-hardening compositions therein are selectively hardened. For example, irradiation with blue light hardens the yellow microcapsules containing the precursor of yellow pigment, irradiation with green light hardens the magenta microcapsules containing the precursor of magenta pigment and irradiation with red light hardens the cyan microcapsules containing the precursor of cyan pigment.
It will be appreciated that, when irradiating the above described sheet of photo-sensitive material with a light image of a color picture, the light of the color picture is suitably analyzed into the three primary colors of red, green and blue and the sheet of photo-sensitive material is irradiated separately with a red light image, a green light image and a blue light image by which the cyan, magenta and yellow microcapsules, respectively, are selectively hardened in accordance with such images. Then, the irradiated or exposed coating of photo-sensitive microcapsules on the sheet of photo-sensitive material is placed in contact with a sheet of developing paper coated with or containing a developing substance, and the contacting sheets are pressed together so as to rupture the shells of the yellow, magenta and cyan microcapsules that were not substantially hardened by irradiation with light of corresponding wave lengths. The substances containing precursors of pigments are transferred from the ruptured microcapsules to the facing surface of the sheet of developing paper and react with the developing substances thereon for developing the respective color pigments from the precursors thereof. Thus, the transferred precursors of pigments from the yellow, magenta and cyan microcapsules are developed into the respective pigments which are suitably mixed to present a printed color picture on the sheet of developing paper.
In a known apparatus for pressing together the sheets of developing paper and photo-sensitive material, as indicated at a on FIG. 1, the sheet c of the photo-sensitive material, which is desirably in the form of a long web or film, and a sheet d of the developing paper are passed together between a pair of vertically superposed cylindrical pressure rollers e and f having axial lengths somewhat greater than the width of the sheets c and d. The lower pressure roller e is rotatably mounted in a suitable support frame (not shown) and rotated by a motor (also not shown). The upper pressure roller is rotatably mounted in a vertically movable frame which is pressed downward by one or more strong resilient members (not shown) so that roller f is pressed downwardly against roller e. A frame or area of the web or sheet c of photo-sensitive material is exposed to a light image before being brought together with the sheet d of developing paper, whereupon the sheets c and d are fed together between the pressure rollers e and f. As the lower roller e is rotated, the upper roller f pressed there-against is also rotated so that the sheet c of photo-sensitive material and the sheet d of developing paper are moved together while being pressed between the rollers e and f.
The apparatus a according to the prior art has the advantage of providing a relatively high printing speed by reason of the fact that the sheets of developing paper and photo-sensitive material are pressed together while being continuously transported or advanced by the rotated rollers e and f. However, in the known apparatus a, the rollers e and f act to press together the sheets c and d simultaneously along a stripe-like area extending across the entire width of the sheets. Therefore, in order to provide the requisite pressure at each increment of such stripe-like area for ensuring the rupture of those microcapsules that have not been fully hardened, and further for ensuring the transfer of the precursors of pigments from the ruptured microcapsules to the sheet of developing paper, a very large force must be provided to urge the roller f toward the roller e. For example, in order to rupture the unhardened microcapsules of the sheet of photo-sensitive material and to ensure adequate contact of the released pigment precursors with the developing substances on the sheet of developing paper, it is necessary that the sheet c of photo-sensitive material and the sheet d of developing paper be pressed together with a pressure of 30 to 40 kg/mm.sup.2. In the case where, for example, a picture is to be printed on a sheet of developing paper of A4 size which has a width of 21 cm, and the rollers e and f employed for pressing together the sheets c and d each having a diameter of 50 mm, the force urging together the rollers has to be about 57 kg for each cm of roller length, that is, a total force of about 1200 kg for rollers having lengths of 21 cm. The apparatus a, in order to be capable of applying such a large force for urging together the rollers e and f, must be massive and requires a high-powered motor and transmission mechanism for transmitting the torque the torque to the lower pressure roller e. As a result of the foregoing, the apparatus a is relatively expensive and difficult to assemble and maintain.
In order to overcome the foregoing disadvantages of the known apparatus a, an apparatus b has been proposed which, as shown in FIG. 2, comprises a fixed back-up member g defining an upwardly facing back-up surface g', and a pressing member h having a spherical ball i rotatably mounted at its lower end. The sheets c and d of photo-sensitive material and developing paper, respectively, are brought into contact with each other and transported intermittently across the back-up surface g' in a direction of sheet travel that is transverse to the length of the back-up surface g'. The pressing member h is mounted for reciprocal movements in the direction along the back-up surface g', that is, perpendicular to the direction of sheet travel, between terminal positions h.sub.1 and h.sub.2, shown in dot-lines of FIG. 2, and at which the pressing member h is situated laterally beyond the side edges of the sheets c and d. During its movements between the terminal positions h.sub.1 the back-up surface g', the pressing member h is urged downwardly so that the ball i exerts pressure for urging together the sheets c and d against the back-up surface g' progressively along a narrow pressing region extending across the entire width of the contacting sheets c and d. The described pressing step is effected repetitively with intervening sheet transporting steps during each of which the sheets c and d are incrementally advanced.
Since the ball i of the pressing member h acts, at any time, against only a very small area of the contacting sheets c and d, the requisite pressure for ensuring the rupture of the unhardened microcapsules and the transfer of the released pigment precursors into adequate contact with the developing substances can be achieved with only a moderate force urging the pressing member h toward the back-up surface g'. Thus, the apparatus b can be relatively compact and light in weight. However, the apparatus b is disadvantageous in that its printing speed is low because the developing of the picture is effected by alternating the movements of the pressing member h across the contacting sheets c and d and the intermittent transporting of the sheets c and d of the photo-sensitive material and the developing paper. Furthermore, as shown on FIG. 3A, the contact pressure between the ball i of the pressing member h and the back-up surface g' is not uniform across the width w of the pressing area, as indicated by the pressure distribution curve j. As will be apparent from such curve j, the contact pressure between the ball i and the back-up surface g is highest at the center of the ball and is reduced therefrom toward the opposite sides of the pressing area.
Therefore, the pressure urging together the sheet c of photo-sensitive material and the sheet d of developing paper d is highest at the center of the pressing area and is progressively reduced towards the opposite margins of such area. Therefore, for any particular degree of exposure, more of the microcapsules will be ruptured for releasing the respective pigment precursors along the center of the pressing area than along the opposite side margins thereof. Thus, the concentration of development on the sheet d of developing paper is highest at the center of each of the stripe-like pressing regions and is gradually reduced or diminished toward the opposite edges of each such pressing region or area, as indicated by the successive concentration distribution curves k on FIG. 3B. If the sheets c and d are intermittently transported through an incremental distance or pitch equal to the width w of the stripe-like area of contact of the ball i with the sheet d of developing paper, the printed or developed picture will have a striped pattern resulting from the irregular concentration of development.
Of course, if the incremental movements of the intermittently transported sheets c and d are reduced, for example, if each incremental movement of the sheets c and d is made equal to about one half the width w of the stripe-like area of contact of the ball i with the sheet d of developing paper, the pressing member h will act on the sheets c and d along overlapping pressing areas with the result that the developed or printed picture will have a more uniform concentration of development on the sheet d of developing paper, as indicated by the concentration distribution curves k on FIG. 3C. However, such reduction of the incremental movements of the sheets c and d will very substantially increase the printing or developing time and thereby considerably reduce the printing speed.
In order to reduce the force that needs to be exerted for pressing together the sheets c and d, as compared with the apparatus a of FIG. 1, while increasing the width of the pressing area along which the sheets c and d are pressed together during each stroke or scan across the width thereof, as compared with the apparatus b of FIG. 2, it has been proposed, for example, as in the pending U.S. patent application identified by Curtis, Morris & Safford U.S. Ser. No. 248,373, and corresponding to Japanese Patent Application No. P270758/87, filed Oct. 27, 1987 and having a common assignee herewith, to replace the pressing member h having a rotatable ball i for contact with the sheet d of developing paper, by a rotatable roller 1 (FIG. 4) disposed in opposing relation to the back-up surface g' and having an axis of rotation extending parallel to the direction of travel of the sheets c and d across the back-up surface g'. The roller 1 has a cylindrical peripheral surface and is mounted for bodily movements relative to the back-up member g parallel to the back-up surface g' in directions perpendicular to the direction of intermittent sheet travel, and during such movements of the roller 1, the latter is urged toward the back-up surface g' with the sheets c and d of photo-sensitive material and developing paper being in contact with each other between the roller 1 and the back-up surface g' so as to be pressed together thereby. By reason of the cylindrical peripheral surface of the roller 1, the width of the stripe-like pressing area along which the sheets c and d are pressed together sufficiently to uniformly develop the picture can be substantially increased. Therefore, the printing or developing speed can be increased relative to that of the apparatus b of FIG. 2.
In the apparatus of FIG. 4, during each incremental movement of the sheets c and d, the roller 1 is moved off the contacting sheets c and d to a standby position on the back-up surface g' at one side or the other of the sheets c and d, as shown on FIG. 5. At the completion of each incremental movement of the sheets c and d, the roller 1 is moved from its standby position on the back-up surface g' at one side of the path of travel of the sheets c and d laterally across the contacting sheets in a pressing step to a standby position on the back-up surface g' adjacent the opposite sides of the sheets c and d, whereupon an incremental movement of the sheets c and d is effected in another sheet transporting step. Thus, the sheet pressing and transporting steps are alternately performed in a repetative manner and, due to the relatively wide area along which the roller 1 can exert the requisite pressure against the contacted sheets c and d during each pressing step, a sufficiently high printing or developing speed can be realized. However, the contacting sheets c and d have a substantial thickness and, as shown on FIG. 5, the opposite side edges of the contacting sheets extend upwardly from the back-up surface g' at the standby positions of the roller 1. Therefore, each time the roller 1 is rolled onto or off the contacting sheets c and d from or to, respectively, a standby position of the roller on the back-up surface g', the roller 1, in effect, rolls over a step and thereby generates objectionable noise. Further, there is the likelihood that, in moving from a standby position on the back-up surface g' onto the contacting sheets c and d, the roller 1 will damage the side edges of the developing paper and the photo-sensitive material, or even that the roller 1, in colliding with the raised side edges of the sheets c and d, will have its rolling movement halted thereby.